With the advent of better multi-channel audio technology for movie soundtracks encoded in formats such as DTS, DOLBY DIGITAL®, DVD Audio, DVD-A, Super Audio Compact Disc, SACD, and the like, surround-sound speakers capable of producing wide dispersion output have been in increasingly high demand for both auditorium and home theatre applications. Surround speaker requirements include diffuse dispersion in the horizontal plane to blur the time arrivals to the listener's ear. This concept is referred to as “reverb.” The audio source may be music, a sound effect, or the like. Multiple speakers can be grouped together to provide a wide dispersion of sound, but there is a nontrivial likelihood that the interaction between such acoustic sources will be acoustically destructive, degrading the sound quality heard by a listener.
Ideally, a point source solution is the answer to this difficulty, but due to size limitations (i.e., most compression drivers are roughly cylindrical with outside diameters between about 5 and 8 inches, making close placement difficult) and limitations of power output capabilities, such a design is impractical and unfeasible in most working applications. Accuracy and intelligibility of acoustic signal is a result of the way the loudspeaker reconstructs the temporal and spectral response of the reproduced wave front. Phase coherence of the signal or wave front is a result of the temporal response when reconstructed. A number of difficulties arise when attempting to sum acoustic wavefronts from multiple drivers including standing waves interference and constructive/destructive amplitude interference caused by overlapping polar patterns between mutually driven acoustic sources.
In practice, the surround-sound speaker design has generally been approached by providing a di-, bi- or tri-polar speaker with 180 degrees dispersion in the horizontal axis. The difficulty with this design is that most transducers tend to narrow the dispersion angle as the wavelength of the output becomes smaller than the area of the transducer mouth and continues to narrow even more as the wavelength becomes smaller than the diameter of the voicecoil. This effect is referred to as “beaming”. The waveguide geometry and/or the throat dimension of the compression driver and/or the diaphragm area of a dome tweeter, along with voicecoil diameter considerations, are the primary contributors to beaming. To avoid beaming, multiple transducers can be used in an arc or array to maximize the dispersion angle in the horizontal axis at the higher frequencies. Unfortunately, in some cases, the complication in this approach is that the polar patterns of dispersion tend to overlap or mesh at the lower frequencies, and thus do not sum acoustically as one wavefront in the axis wherein the transducers are placed due to polar patterns. The polar patter overlapping give rise to constructive/destructive interference, which is interpreted by the listener as a reduction in fidelity and sound quality. Therefore, beaming is reduced at the higher frequencies at the expense of sound quality from an incoherent wavefront reconstruction.
There are other horn designs wherein multiple transducers are arrayed and have polar patterns that match the desired effect of having a wide, consistent polar pattern, even at higher frequencies. The drawback is that the resultant configurations do not even approximate the desired flat front of the horn.
There are horns known in the art that have been developed to provide skewed areas of sound output. One such horn 1 is shown in FIG. 1, and uses a diffraction slot and throat geometry to increase the angle through which the sound output is directed. However, in many applications, such as home theater systems, it is desirable that the speakers be recess-mounted such that the speaker mouth is flush with the wall, and the mouth of the horn 1 of FIG. 1 is not flat. Skewed-angle dispersion loudspeaker horns have been developed to provide dispersed sound output through a flat or substantially flat mouth, and one such horn 2 is illustrated in FIGS. 2A-2B. The prior art horn of FIGS. 2A-2B utilizes a diffraction slot of variable width to skew the sound energy output off axis. However, the known prior art horns 1, 2 tend to have a maximum dispersion or skew angle of about 30 degrees. Further, these horns 1, 2 tend to not skew high frequency sound with wavelengths shorter than the throat dimension of the horn 1, 2. Additionally, the area expansion of the horn near the mouth has been abruptly truncated to provide a flat front. This can alter the amplitude response and polar pattern of the transducer.
Thus, there remains a need for a flat-mouth surround-sound speaker design that can provide surround-sound through a consistent and un-truncated area of expansion, through wider skew angles and over wider frequency ranges without experiencing both beaming and destructive interference. The present invention addresses this need.